Display systems, such as televisions, display full-motion video images as a series of still frames. Each frame of the image is comprised of a two-dimensional array of picture elements, known as pixels, arranged in orthogonal rows and columns. The image information is transmitted in a raster-scan format, one line at a time from top to bottom. Within each line the pixel information is transmitted from left to right.
In some embodiments of television systems, no cathode ray tube (CRT) is used. These televisions use arrays of individually controllable elements, such as liquid crystal devices (LCDs), or digital micromirror devices (DMDs). Because there is no scanning gun in these systems, they will put the entire frame onto the activation circuitry for the array of individual elements.
Standard television systems in the United States have 480 rows with a resolution of approximately 572 pixels in each row. Video Graphic Adapter (VGA) standards specify an image comprised of 480 rows of 640 pixels and Extended Graphic Adapter (XGA) standards specify an image comprised of 1024 rows of 768 pixels.
Recent standards have been developed for high-definition television (HDTV). For example, an HDTV signal can carry 1,080 rows of 1,920 pixels at 24, 30 and 60 Hz refresh rate progressive video with 720 rows of 1,280 pixels with refresh rates at 24, 30 and 60 Hz. The higher resolution, interlaced format presents 2,073,600 individual pixels for each frame, and the lower resolution, progressive format presents 921,600 individual pixels. There are plans to update HDTV using progressive scan technology combined with the 1,080 by 1,920.